IMS architecture overview
An overview of IMS architecture and related Accenture experiences.
Università Federico II - Napoli, 27 aprile 2007
Copyright © 2007 Accenture All Rights Reserved. Accenture, its logo, and High Performance Delivered are trademarks of Accenture.
Agenda
• Introduction
• IMS and Telecommunications Operators services
• IMS architecture
• IMS Call Flow
• Developing services within IMS
• IMS evolution: TISPAN architecture
• IMS role in Operators technology roadmaps
Copyright © 2007 Accenture All Rights Reserved.
2
Introduction
The presentation gives an overview of IMS architecture, including how it can help
telecommunication operators to achieve their goal of delivering advanced and
innovative services, with reference to Accenture International experiences within
incumbent, large and minor TelCos.
The main topics discussed are:
- IMS and Telecommunications Operators services
What is IMS and why it is important for TelCo
- IMS architecture
Elements, funtions, protocols and standards behind IMS
- IMS role in Operators technology roadmaps
How TelCo drives their business towards IMS solutions
- Accenture clients and IMS: some highlights
IMS experience and VoIP solutions in major Accenture clients
Copyright © 2007 Accenture All Rights Reserved.
3
Agenda
• Introduction
• IMS and Telecommunications Operators services
• IMS architecture
• IMS Call Flow
• Developing services within IMS
• IMS evolution: TISPAN architecture
• IMS role in Operators technology roadmaps
Copyright © 2007 Accenture All Rights Reserved.
4
IMS Architecture overview
In essence, what is the IP Multimedia Subsystem?
The IP Multimedia Subsystem (IMS) provides a unified
service architecture for all networks, leveraging the
capabilities of IP.
IMS
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5
What drives IMS Deployment?
There are both business and technical drivers associated with IMS deployment, that
will bring benefits in service creation capabilities as well as in cost optimization
Increase
Revenue
Control
CapEx
BUSINESS DRIVERS
IMS offers richer user
experience with
sophisticated business
models
Value Chain
Positioning
Copyright © 2007 Accenture All Rights Reserved.
TECHNICAL DRIVERS
IMS is able to deliver services
faster, at lower cost
and independently of
devices, access
and media types
Convergence
Service
Enhancements
Lower
OpEx
6
IMS and Service Enhancements: main keywords
IMS enables a packet-based network to provide multiple services
on single Control/Service Layers via different access network.
— Main characteristics —
— Reference architecture —
To
From
• Access agnostic
VoIP
User
DB
• Services independent
Mail VoD
…
Integrated services platforms
video
data
voice
Services
Control
• Open architecture
IM
IP
Transport
• Multi-device
Physical Network
Physical Network
• Vendor independent
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IMS enabled
7
A controlled path from separate infrastructures to all-IP
and IMS
A (controlled) change of paradigm in the network architectures is a
clear requirement for achieving the goal of delivering advanced
and innovative services in an efficient way
Wireline access
IMS
Wireline
access
Wireless
access
Wireless
access
Services
services tightly associated with specific
terminals and access networks
layered networks with separated, non integrated service control layers
non-uniform user profiling
IP pervasive but issues in guaranteeing QoS
and charging for real-time, integrated
services
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Services
IMS introduces a structured, layered architecture
with “standardized” interfaces
clear path for integrating 3G world and “internet”
ubiquitous access to all services from any
device: IMS as access independent and all
services developed on IMS are access agnostic
uniform support for customer profiling, service
access control and charging, integration with
“legacy” networks
8
Agenda
• Introduction
• IMS and Telecommunications Operators services
• IMS architecture
• IMS Call Flow
• Developing services within IMS
• IMS evolution: TISPAN architecture
• IMS role in Operators technology roadmaps
Copyright © 2007 Accenture All Rights Reserved.
9
IMS architecture
The IP Multimedia Subsystem is an architecture, originally defined
and standardized by the 3GPP consortium, thought to provide
multimedia services exploiting an ALL-IP domain.
IP transport offers a cheaper and simpler way to carry multimedia sessions, compared to traditional
circuit-switched networks.
A first step toward the all-IP solution is the separation of the Control Layer from the
Transport Layer, which can therefore be implemented exploiting the IP network
IMS steps over, redefining and standardizing the
Transport Layer, Control Layer and
Application Layer to exploit the IP
infrastructure
The IMS solution is therefore an ALL-IP
architecture. Moreover standardization of
functions and interfaces allows:
Interoperability with other providers
Convergence of services
Flexibility and extensibility of the solution
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ALL-IP Network
Application
Layer – IP based
Control Layer –
IP based
Transport Layer –
IP based
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IMS Overview:
Standardization Organizations
The 3rd Generation Partnership Project (3GPP) is a collaboration agreement that was established in
1998 bringing together a number of telecommunications standardization bodies. Scope of 3GPP was to
produce globally applicable Technical Specifications and Technical Reports for a 3rd Generation Mobile
Systems based on GSM, GPRS and EDGE core networks and the radio access technologies.
The European Telecommunications Standards Institute (ETSI) is an independent, non-profit organization, whose mission is to
produce telecommunications standards for today and for the future. responsible for standardization of Information and
Communication Technologies (ICT) within Europe
European Telecommunications Standards
Institute is an independent, non-profit
organization, whose mission is to produce
telecommunications standards for ICT within
Europe
Asian Association of Radio
Industries and Businesses, to
conduct research & development
on utilization, realization and
popularization of new radio
systems in telecommunications
and broadcasting.
China Communication Standards
Association, to contribute to the
development of information industry
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Alliance for Telecommunications Industry
Solutions (ATIS) is a U.S.-based
organization that is committed to rapidly
developing and promoting technical and
operations standards for the communications
ETSI
ARIB
ATIS
3GPP
CCSA
Japanese Telecommunication
Technology Committee, with the
purpose of contributing to
standardization in the field of
telecommunications by
establishing protocols and
standards
TTC
TTA
TTA (Telecommunications Technology
Association) is an IT standards organization
that develops new standards and provides
one-stop services for the establishment of IT
standards as well as providing testing and
certification for IT products
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IMS layers and functions : overview
The resulting IMS architecture defines
elements and functions on three layers:
MAP
Application
Layer
OSA-AS
SIP-AS
OSA - API
ISC
OSA-SCS
ISC
CSE
CAP
SIP
ISC
IM-SSF
Si
Dh
Control
Layer
SLF
S-CSCF
Dx
SIP
Mw
Mg
SIP
Sh
HSS
DIAMETER
Access and
Transport Layer
Cx
I-CSCF
DIAMETER
SIP
Mw
Gm
SIP
P-CSCF
Mi
BGCF
Mj
MGCF
Mr
MRFC
SS7
over IP
SGW
Mn
SS7 MTP
H.248/
Megaco
H.248/
M p Megaco
INTERNET
IP Core
GGSN
UTRAN Network GGSN
Fixed Network
MRFP
BRAS
BRAS
MGW
PSTN/
PLMN
DSLAM
DSLAM
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IMS Core Network Element : CSCF
Call session control function
Several types of SIP servers known as CSCF are used to
process SIP signaling packets in the IMS domain:
Proxy CSCF
Interrogating CSCF
Serving CSCF
The CSCF elements are responsible for SIP session control and implements the logics for the following
functions:
user authentication
call routing
controlling the generation of call detail records (CDRs) for accounting purposes
Each network will typically have multiple CSCFs of each type, allowing load sharing and supporting
increased reliability through the use of backup servers.
All the CSCF will use the session initiation protocol (SIP) as signaling protocol. Interaction with other
domains using different protocols are performed by dedicated elements which allow protocol translation.
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IMS Core Network Element : P-CSCF
Proxy Call Session Control Function
A P-CSCF is the first point of contact for the IMS terminal, and performs
the following main functionalities:
forwards the registration requests received from the UE to the I-CSCF
forwards the SIP messages to the S-CSCF that administrate the user, whose address
is defined during the registation
forwards the request and the answers to the UE
The P-CSCF is assigned to an IMS terminal during registration, assigned either via DHCP, or in the
PDP Context, and does not change for the duration of the registration.
Sits on the path of all signalling messages, and can inspect every message
Authenticates the user and establishes an IPsec security association with the IMS terminal. This prevents spoofing
attacks and replay attacks and protects the privacy of the user.
Can compress and decompress SIP messages using SigComp, which reduces the round-trip over slow radio links
May include a PDF (Policy Decision Function), which authorizes media plane resources e.g. quality of service (QoS)
over the media plane. It's used for policy control, bandwidth management, etc ... The PDF can also be a separate
function.
Can be located either in the visited network (in full IMS networks) or in the home network (when the visited network is
not IMS compliant yet).
Some networks might use a Session Border Controller for this function.
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14
IMS Core Network Element : I-CSCF
Interrogating Call Session Control Function
An I-CSCF is a SIP function located at the edge of an
administrative domain.
its IP address is published in the DNS of the domain (using NAPTR and
SRV type of DNS records), so that remote servers can find it, and use it
as a forwarding point (e.g. registering) for SIP packets to this domain.
its IP address is published in the DNS of the domain (using NAPTR and SRV type of DNS records), so
that remote servers can find it, and use it as a forwarding point (e.g. registering) for SIP packets to this
domain.
I-CSCF queries the HSS using the DIAMETER Cx interface to retrieve the user location (Dx interface
is used from I-CSCF to SLF to locate the needed HSS only), and then routes the SIP request to its
assigned S-CSCF.
Up to Release 6 it can also be used to hide the internal network from the outside world (encrypting part
of the SIP message), in which case it's called a THIG (Topology Hiding Inter-network Gateway).
From Release 7 onwards this "entry point" function is removed from the I-CSCF and is now part of the
IBCF (Interconnection Border Control Function). The IBCF is used as gateway to external networks,
and provides NAT and Firewall functions (pinholing).
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15
IMS Core Network Element : S-CSCF
Serving Call Session Control Function
An S-CSCF (Serving-CSCF) is the central node of the signalling
plane.
It is a SIP server always located in the home network. The S-CSCF uses
DIAMETER Cx and Dx interfaces to the HSS to download and upload user
profiles - it has no local storage of the user.
All necessary information is loaded from the HSS.
it handles SIP registrations, which allows it to bind the user location (e.g. the IP address of the
terminal) and the SIP address
it sits on the path of all signaling messages, and can inspect every message
it decides to which application server(s) the SIP message will be forwarded, in order to provide their
services
it provides routing services, typically using ENUM lookups
it enforces the policy of the network operator
there can be multiple S-CSCFs in the network for load distribution and high availability reasons. It's the
HSS that assigns the S-CSCF to a user, when it's queried by the I-CSCF.
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IMS Core Network Element : HSS or UPSF
Home Subscriber Server or User Profile Server Function UPSF
The HSS is the database of all subscriber and service data.
HSS is the master user database that supports the IMS network entities that
handle the call sessions:
it contains the subscription-related information (user profiles), used by the
control layer
It contains subcription information used by the service layer
it provides data used to perform authentication and authorization of the user
it can provide information about the physical location of user
The HSS also provides the traditional Home Location Register (HLR) and Authentication Centre (AUC)
functions. This allows the user to access the packet and circuit domains of the network initially, via IMSI
authentication.
User Profile is composed by:
user identity
allocated S-CSCF name
Registration information and roaming profile
authentication parameters
Control and service information.
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17
IMS Core Network Element : SLF
Subscription Locator Function
An SLF is needed to map user addresses when multiple HSSs
are used.
The Subscription Locator Function (SLF) is used in a IMS network as a
resolution mechanism that enables the I-CSCF, the S-CSCF and the AS to
find the address of the HSS that holds the subscriber data for a given user
identity when multiple and separately addressable HSSs have been deployed
by the network operator.
The SLF expose Dx and Dh interfaces, which have the same syntax and semantic of the Cx and Sh
interfaces provided by the HSS.
The SLF does not perform any logic on its interfaces, but replies to the requestor with a REDIRECT
message, specifying the address of the HSS which is able to fulfill the request received.
Both the HSS and the SLF communicate through the DIAMETER protocol.
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18
IMS Core Network Element : MRF
Media Resource Function
An MRF is a source for network initiated and network
managed media streams in the home network.
It is exploited for :
– Playing of announcements (audio/video)
– Multimedia conferencing (e.g. mixing of audio streams)
– Text-to-speech conversion (TTS) and speech recognition.
– Realtime transcoding of multimedia data (i.e. conversion between different codecs)
Each MRF is further divided into :
– An MRFC (Media Resource Function Controller) is a signalling plane node that acts as a SIP
User Agent to the S-CSCF, and which controls the MRFP with a H.248 interface
– An MRFP (Media Resource Function Processor) is a media plane node that implements all
media-related functions.
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19
IMS Core Network Element : BGCF
Break Out Gateway Control Function
The Breakout Gateway Control Function is the IMS element
that selects the network in which PSTN breakout has to
occur.
A BGCF is used for calls from the IMS to a phone in a Circuit
Switched network, such as the PSTN or the PLMN.
BGCF forwards the signaling to the selected PSTN/PLMN network.
If the breakout occurs in the same network as the BGCF then the BGCF selects a MGCF
(Media Gateway Control Function) that will be responsible for inter-working with the PSTN,
and forwards the signaling to MGCF. Otherwise it forwards signaling to BCGF of another
operator network
The MGCF then receives the SIP signalling from the BGCF and manages the interworking
with the PSTN network.
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20
IMS Core Network Element : PSTN Gateways
Public Switched Telephony Network Gateways
The interworking with the Circuit Switched network is realized by
several components, for signaling, media and control
functionalities:
SGW (Signalling Gateway)
is the interface with the signaling plane of the Circuit Switched Network (CS).
It transforms lower layer protocols as SCTP (which is an IP protocol) into MTP
(which is a SS7 protocol), to pass ISUP from the MGCF to the CS network.
MGCF (Media Gateway Controller Function)
– Performs call control protocol conversion between SIP and ISUP
– interfaces the SGW over SCTP
– controls the MGW resources with a H.248 interface.
•MGW (Media Gateway)
– Interfaces the media plane of the CS network, by converting between RTP
and PCM.
– It can also perfom media transcoding, when the codecs used do not match
(e.g. IMS might use AMR, PSTN might use G.711).
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21
IMS Core Network Element : AS
Application Servers
Application Servers host and execute services, and interface with
the S-CSCF using SIP.
This allows third party providers an easy integration and deployment of their
value added services to the IMS infrastructure.
Examples of services are:
– Caller ID related services (CLIP, CLIR, ...)
– Call waiting, Call hold, Call pick up
– Call forwarding, Call transfer
– Call blocking services, Malicious Caller Identification
– Lawful interception
– Announcements, Digit collection
– Conference call services
– Location based services
– SMS, MMS
– Presence information, Instant messaging
– Voice Call Continuity Function (VCC Server) or Fixed Mobile Convergence
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22
IMS Core Network Element : IM-SSF
IP Multimedia - Service Switching Function
The IM-SSF is the node in the IMS domain which provides interworking between the SIP session control and the Intelligent
Network of traditional networks.
It allowing service requests to be forwarded to legacy service delivery platforms
such as IN-based SCPs.
IM-SSF provides intelligent gateway functionality between the SIP-based IMS
network and IN systems that use protocols such as CAMEL, INAP, AIN and MAP
This functionality is critical for the rollout of new, converged offerings, while
continuing service to high-value customers.
The IM-SSF also enables access to subscriber information retrieved from the
HSS over the Si interface using the MAP protocol.
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23
IMS Core Network Element : Service Layer
Interfaces
The IMS control layer implements several interfaces toward the service layer which enables the user
to access to service logics implemented by heterogeneous resources and application servers.
IMS Operator
3rd Party Service
Provider
Third Party
Services
OSA
Compliant
Services
IN legacy
Services
SIP
Services
OSA AS\
OSA AS
CSE/
IN legacy
SIP AS
(OSA API)
(OSA API)
Diameter
(Sh interface)
CAP
(Si Interface)
OSA
Gateway
IM-SSF
SIP
(ISC interfcae)
SIP
(ISC Interface)
S-CSCF (IMS Call Control Function)
SIP
(ISC interface)
HSS
Diameter
(Cx interface)
– ISC (between S-CSCF and OSA Gateway/IM-SSF/SIP AS) allows to receive/notify SIP messages from/to
the S-CSCF to realize the service session control
– Cx beetwen S-CSCF and HSS is used to retrieve/update the subscriber profile data
– Sh between HSS/OSA- Gateway/SIP-AS is used to retrieve/update the subscriber profile data related to
the service. The HSS is responsible for policing what information will be provided to each individual
application server.
– Si between HSS and IM-SSF is used to retrieve/update the subscriber profile data related to IN services
Copyright © 2007 Accenture All Rights Reserved.
24
Agenda
• Introduction
• IMS and Telecommunications Operators services
• IMS architecture
• IMS Call Flow
• Developing services within IMS
• IMS evolution: TISPAN architecture
• IMS role in Operators technology roadmaps
Copyright © 2007 Accenture All Rights Reserved.
25
Example: Registration and Basic Call Flow
IMS
domain A
UE 1
UE 2
S–CSCF
S–CSCF
Registration
Before starting a multimedia session, the
UE must register to the IMS domain.
I–CSCF
HSS
S–CSCF
P–CSCF
I–CSCF
HSS
UE 1
P–CSCF
UE 2
IMS domain B
UE 3
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26
Example: Registration and Basic Call Flow
Session set up
UE in different IMS domain
IMS
domain A
UE 1
UE 2
I–CSCF
The session origination procedures specify the
signaling path between the UE initiating a
session setup attempt and the Serving-CSCF
that is assigned to perform the session
origination service. This signaling path is
determined at the time of UE registration, and
remains fixed for the life of the registration.
P–CSCF
S–CSCF
S–CSCF
S–CSCF
HSS
I–CSCF
HSS
UE 1
P–CSCF
UE 2
IMS domain B
UE 3
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27
Example: Registration and Basic Call Flow
Session set up
UE in the same IMS domain
IMS
domain A
UE 1
UE 2
S–CSCF
S–CSCF
The session origination procedures specify the
signaling path between the UE initiating a
session setup attempt and the Serving-CSCF
that is assigned to perform the session
origination service. This signaling path is
determined at the time of UE registration, and
remains fixed for the life of the registration.
I–CSCF
HSS
S–CSCF
P–CSCF
I–CSCF
HSS
UE 1
P–CSCF
UE 2
IMS domain B
UE 3
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28
Example: Call Flow with services :
Call Barring and Number Portability
User A initiates a call to a number that has been ported to an external network.
User A has the Call Barring service, which prevents him to call 1xx numbers, hence the S-CSCF triggers the
Application Server to apply the CB logic. The AS retrieves the profile associated to User A from the HSS,
perform the service logic, and sends back the message to the S-CSCF allowing the call.
Call control comes back to the CSCF,
which interrogates the HSS and
recognizes the dialed number has been
‘ported’ to an external network. The SCSCF forward the request to the IM-SSF
to apply the Number Portability service
on the Intelligent Network.
Number
Portability
The CSCF completes the signaling
phase forwarding the call to the BGCP,
and finally to the called party User B.
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IM-SSF
IN
INSCP
SCP
AS
Si
The IM-SSF forwards the request to the
SCP using INAP, which responds with
the new Routing Number of the User B.
The IM-SSF responds to the S-CSCF
with the new number.
Call
Barring
INAP
ISC
Sh
ISC
BGCF
P-I-S-CSCF
U.A. B
U.A. A
Cx
HSS
29
Agenda
• Introduction
• IMS and Telecommunications Operators services
• IMS architecture
• IMS Call Flow
• Developing services within IMS
• IMS evolution: TISPAN architecture
• IMS role in Operators technology roadmaps
Copyright © 2007 Accenture All Rights Reserved.
30
Developing and deploying applications
• Applications deployed on ASs are the basic blocks used to develop services.
• Services can be provided directly by a single application or can be the result of the orchestration of
several applications, eventually hosted on different Application Servers.
• Application Servers are the execution environments for applications, providing framework facilities
such as protocols and interface support, database connections, security, monitoring and more…
Application Server
NB i/f
BSS i/f
BSS
Charging
Presentation Interfaces
APIs
Execution Environment
Connectors
Protocols
DB Connections
Libraries
Conn Pools
SB i/f
Security
Performnance
Assurance
Configuration
Fault Mgmt
Applications
Applications
Applications
Data
Data Layer
OSS
Service Logics
Layer
DB i/f
OSS i/f
Listeners
Southbound systems
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31
SLEE and Servlet-Container architectures
• Application Containers can be based on different paradigms, depending on the structure of the
application execution environment and on the technique used to convey messages between different
components inside the application server.
Two main execution environments types are currently exploited to develop application servers:
Message Driven, Servlet Containers
Event Driven, SLEE
Synchronous execution:
• Logics are activated by requests received
from the network
Asynchronous execution
• Requests generate events. Service logics
are notified of raised events, and activate
services
Service model: Request/response
• Direct association between messages and
logics
Service model: Publish/subscribe
• Requests have not a direct connection with
service blocks
Coarse grained (‘Grana grossa’)
• Does not allow to manage same request in
different way
Fine grained (‘Grana Fine’)
• Allows more granularity in management of
the requests
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32
Application Architectures: SLEE
SLEE (Service Logic Execution Environment) architecture is based on an execution model with
application hosted as independent service building blocks (SBB).
Each SBB can be triggered and activated by one or more events, generated inside the SLEE
Interfaces are realized implementing Resource Adaptors, which manage listeners and protocols, and
are able to raise specific events when interrogated by network requests.
The SLEE environments manages the entire lifecycle of events, applying subscribe/notify and routing
rules between RAs and SBBs.
SLEE Container
This kind of service environment has been
specifically thought for TelCo operators, as
allows following features:
Modular development of service logics
Easy combination of different Service
Block to provide convergent services
Resource Adapters can be added or
extended without modifying the service
logics implemented inside SBBs
SBB
SBB
SBB
SBB
Event Dispatcher
Events Collector
Resource
Adapter
Resource
Adapter
Resource
Adapter
External system
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33
Application Architectures: Servlet Containers
Servlet Containers are execution environments which bind the execution of a service logic to the
receiving of a particular request.
Service Logic lifecycle is entirely managed by the environment
Requests are associated to service logics depending on the type of message received (servlet model)
Service Logics are activated synchronously with request elaboration
Combination of service logics is managed redirecting messages inside the container
Servlet Container
The servlet paradigm can be used
implementing adaptors for several protocols,
allowing the development of fast network
oriented services:
Service Logics are directly connected to
network messages
Can manage queuing, overloading and
prioritization of requests
Protocols and interfaces can be added
implementing new listeners
Service
Service
Service
Service
Execution
queue
Execution
queue
Execution
queue
Execution
queue
Protocol
Listener
Protocol
Listener
Protocol
Listener
External system
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34
Agenda
• Introduction
• IMS and Telecommunications Operators services
• IMS architecture
• IMS Call Flow
• Developing services within IMS
• IMS evolution: TISPAN architecture
• IMS role in Operators technology roadmaps
Copyright © 2007 Accenture All Rights Reserved.
35
IMS evolution: NGN Tispan Architecture
The Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN) is a
standardization body of ETSI, specializing in fixed networks and Internet convergence.
TISPAN is the ETSI core competence centre for fixed networks and for migration from switched circuit
networks to packet-based networks with an architecture that can serve in both to create the Next Generation
Network.
•This focus on fixed accesses together with the choice of using the IMS network in the core architecture led to
new requirements and to an evolution of the original IMS solution.
TISPAN and 3GPP are now working together to define a harmonized IMS-centric core for both wireless and
wireline networks, enabling new convergent accesses and services.
3GPP /
IMS
TISPAN
Wireless access
Wireline access
AGW
AGW
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36
IMS evolution: NGN Tispan Architecture
The NGN standard functional architecture, defined by TISPAN, is composed by a “service layer”
and a “transport-layer” both based on IP.
•This subsystem-oriented architecture enables the addition of new subsystems over the time to cover new
demands and service classes. The architecture ensures that the network resources, applications, and user
equipment are common to all subsystems and therefore ensure user, terminal and service mobility to the
fullest extent possible, including across administrative boundaries.
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37
TISPAN – NGN Functional Architecture (2/2)
TISPAN NGN solution is based on a subsystem–oriented architecture, enabling the insertion of
new subsystems over the time to cover new demands and providing the ability to import/adapt
subsystems defined within other standardization bodies.
Transport Layer
Components
IP Connectivity is provided to the user
equipment by the Transport Layer.
The transport layer comprises a transport
control sub layer on top of transfer
functions.
The transport control sub layer
is further divided in two subsystems:
Network Attachment Subsystem
(NASS)
the Resource and Admission
Control Subsystem (RACS).
Service Layer Components
The service layer comprises:
Core IP Multimedia Subsystem (IMS)
PSTN/ISDN Emulation Subsystem
(PES)
Other subsystems (e.g. streaming
subsystem, content broadcasting
subsystem etc.) and applications
Common components used by several
subsystems, such as:
-charging
-user
profile management
-security
-routing
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functions
management
data bases (e.g. ENUM)
38
NASS – Network Attachment SubSystem
NASS is a Transport Control layer element defined by ETSI /
TISPAN
NASS system provides integrated and centralized
management of users access to the network
NASS makes possible to expose towards upper-layer systems users presence informations and at the
same time apply policies to control network access based on varoius users profiles
NASS functionalities cover:
Authentication and authorization
Dynamic or static IP address assignment
Access devices configuration
Assignment of the proxy to access to IMS services (i.e. P-CSCF)
Access parameters management (i.e. QoS, bandwidth )
Management of network presence towards application layers
Mobility features
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39
RACS (Resource and Admission Control
Subsystem)
RACS is the TISPAN element in the transport control layer
responsible of policy control, resource reservation and
admission control.
Racs main functionalities are:
Admission Control, which enforce limitations to the access to
network resources, e.g. applying bandwidth thresholds
Resource reservation, which enable the reservation, for a given
period, of the resources needed to provide a service. For example a
voice call will reserve a given bandwidth over the entire circuit
before the call is initiated
Policy Control, enable enforcement of policies on the resource
exploitation
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40
Agenda
• Introduction
• IMS and Telecommunications Operators services
• IMS architecture
• IMS Call Flow
• Developing services within IMS
• IMS evolution: TISPAN architecture
• IMS role in Operators technology roadmaps
Copyright © 2007 Accenture All Rights Reserved.
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Service-driven Vs. network-driven NGN approach
Program and Project Management
Strategy
Marketing &
Service
Requiremen
ts
Development & Test
Services
and
Network
Architecture
Design
Service
Development
Products Devp
&
Customization
Platforms
and Network
Deployment
Pros
Operational
Excellence
• Launch & Tune
single “buildings
blocks” enabling
services due to
the faced
approach
E2E
Integration
Tests
Roll Out
Operation
Operation
s
Market Trial
deployment
Evolution
Network-driven approach
Service-driven approach
Cost
• Incremental
Effectiveness Capex due to
progressive
services Launch
Market Trial
Cons
• Develop interfaces
between existing
and new networks
elements (low
reusability)
• Multiple complex
network
configuration
required for an
heterogeneous
environment
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Pros
Cons
Cost
• Opex decrease • Costly and
Effectiveness due to an
challenging
integrated and
deployment due to
homogeneous
an “in one swoop”
environment
overhauled network
Operational • Efficient Service • Technologies and
Excellence
Creation and
standards are
Delivery
evolving, products
obsolescence
management
needed
42
IMS role in Operators technology roadmaps
IMS
is going to play a key role in Operators technology context for controlling and enabling the
introduction of innovative/convergent services in an ALL IP environment
IMS is emerging as the de facto convergence model for fixed, mobile and enterprise telephony. IMS
will be used to keep control of the network while using IP technologies: Service and Control Layers
will be implemented using IMS architectures as a key: element to support both IP multimedia
sessions over heterogeneous media type.
IMS architecture will be used as “the” mean for obtaining fixed and mobile convergence (3GPPTISPAN): different IMSs for mobile and fixed networks will be integrated and merged into a
single infrastructure (e.g. single HSS –Data Base for all users)
Innovative and advanced Services (e.g. combinational ones) will leverage convergent IMS-enabled
Service Layer
IMS alone is not enough, it will be complemented with additional functional elements such as:
external interfaces, databases, enablers (presence, location,…), QoS server, media server, IMSenabled terminals
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43
IMS in the existing Provider’s service environment is not
alone…
Service interconnections with legacy and consolidated platforms in the short term
and with non-IMS platforms will be needed to deliver the integrated experience that
users ask for.
Service interconnection
IN Services
PSTN
Services
IMS
IP Services
Packet
Switched
Services
Circuit
Switched
Services
Control
Transport
PSTN
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IP
PLMN
44
…and Service Delivery Platform provides
the needed functions to support IMS
integration and service creation
Service Delivery Platform
3PGW
Service Creation and Execution
Service Orchestration
Service Control
Core Services
IN Services
PSTN
Services
IMS
IP Services
PS
Services
CS
Services
Control
Transport
PSTN
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IP
PLMN
45